Conventionally, a light or radiation image pickup apparatus has a light or radiation detector for detecting light or radiation. Light herein refers to infrared rays, visible light, ultraviolet rays, radiation, gamma rays and so on. An X-ray detector in particular will be described by way of example. As the X-ray detector, a flat panel detector (hereinafter called FPD) is in wide use which detects X-rays using an active matrix substrate. This is because the active matrix substrate is very useful in that X-ray detection values can be read on a pixel-by-pixel basis.
However, with the FPD using the active matrix substrate, time variation noises occurs as circuit noises. This is caused by noises or the like generating from wiring of the active matrix substrate or amplifier circuits. In order to remove these time variation noises, a method has been developed for removing the time variation noises from detection signals by calculating an average value of detection value, as time variation noises, acquired from areas at opposite ends of the FPD not used as pixels for X-ray detection, such as corrective pixel areas arranged in X-ray-shielded areas in a housing sealed with lead, for example.
As disclosed in Patent Document 1, for example, radiation shielding is made perfect in the corrective pixel areas at opposite ends of the FPD by disconnecting thin-film transistor (TFT) circuits and an X-ray conversion layer, to detect time variation noises generating from the TFT circuits, and wiring of the active matrix substrate and the amplifier circuits.
[Patent Document 1]    Unexamined Patent Publication No. 2003-87656